Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$240.52	11.362%	$267.8479	$267.85	$267.85	$267.80
Purchase #2	$63.53	12.685%	$71.5888	$71.59	$71.60	$71.60
Purchase #3	$232.53	10.689%	$257.3851	$257.39	$257.40	$257.40
Purchase #4	$108.89	9.687%	$119.4382	$119.44	$119.45	$119.40
Purchase #5	$74.95	10.789%	$83.0364	$83.04	$83.05	$83.00
Purchase #6	$100.68	10.825%	$111.5786	$111.58	$111.60	$111.60
Purchase #7	$26.44	4.815%	$27.7131	$27.71	$27.70	$27.70
7 purchase totals =	$847.54		$938.5881	$938.60	$938.65	$938.50